In medical images, there are mixed imaging regions corresponding to many areas of an object to be examined such as organs, muscles, fat and bones (hereinafter generically referred to as “organs, etc.”). In such medical images, when a doctor desires to obtain a 3-dimensional image by extracting, for example, only the region showing a liver, there is a method referred to as the region extracting process for extracting only the liver region.
The conventional region extracting process is executed using the region growing method or the threshold value processing method. The region growing method is executed by the following procedure:    (1) An operator selects a region for extracting such as an organ, etc. from the medical image displayed on a screen, and specifies and inputs a point (1˜several pixels) using a mouse on the selected region.    (2) A computer ultimately extracts the entire region of the desired organ, etc. while expanding one point in the region, applying the fact that the pixel value of the surrounding points of the one point in the region of the organ specified by the operator is constant or varies only a slight amount.
However, the region growing method has the problem that excessive region gets extracted in the case that the region that satisfies the extracting condition is arranged adjacent to the desired region, which requires the measures disclosed in Patent Document 1 to be taken.
Patent Document 1 discloses the method for adding restriction on the region expansion by implementing the region growing process only in the region where a region of interest is encompassed and set by a closed curve on a medical image.
Patent Document 1: JP-A-H10-192256
However, the conventional restriction method for region expansion has an unsolved problem that the operator is required to perform a complex operation to accurately encompass the region with a closed curve.